Modern designs of recording heads for magnetic data recording employ thin film technology, where the various elements of the head are created by depositing a number of layers of insulators, magnetic materials and conductors in preselected patterns and with precisely determined relative positions with respect to each other. After fabrication, these heads occupy the trailing end surface of a flyer adjacent the flyer's air bearing surface. Such a head has a flux path comprising top and bottom legs in opposed relationship which form a flux gap adjacent the air bearing surface and which are joined in an area spaced from the flux gap. A winding passes between the legs and between the area where the legs are joined and the flux gap.
The typical head thus created has a flux path with a relatively wide cross section in the area adjacent the winding, which tapers uniformly to a throat section. The throat section can be considered to be the portion of the flux path where the width of each flux path leg is approximately constant and minimum, and the spacing between the legs is decreasing toward the gap. The gap can be defined as the part of the flux path where the width of the legs and their spacing from each other are both minimum. The pole tips form the end of each of the top and bottom legs and are flush with the air bearing surface. The flux gap is defined as the insulating material between the poles. The thickness of each leg is usually less in the neighborhood of the poles than elsewhere in the flux path.
In use, rapid, relative motion between the flyer and an adjacent recording medium surface aerodynamically suspends the flyer above the medium with the head at its flux gap in magnetic coupling relationship with the medium. Magnetic patterns representing data can thus be created in and read from the medium by use of the winding.
Because of the very small dimensions involved, it is not possible during fabrication of individual heads to control the relative dimensions of the patterns in the individual layers or the relative positions of the various layers to better than a few percent of the typical dimensions involved. Furthermore, in such an application, the magnetic materials comprising the flux path are deposited in very thin layers whose thickness and magnetic characteristics are difficult to control during fabrication. These variations can result in unpredictable writing (recording) performance which is not desirable. Designing the flux path so that it saturates somewhere other than at the pole tips during writing keeps the critical pole tip field gradients relatively predictable and substantially reduces this problem. Saturation in a thin film head flux path typically occurs in only one place, since the flux path cross-section normal to flux flow usually has but one minimum area at which saturation occurs, and flux which leaks from the path at this point does not typically reenter the path some other place. These heads frequently saturate in the trailing leg's throat section because thin film fabrication techniques do not easily allow a trailing pole to be wider than the leading pole beneath it, and thicknesses of the two legs are preferred to be nearly the same, so that pole tip lengths (measured perpendicular to the flyer end surface) are equal.
References deemed most pertinent for the invention to be described below are IBM Technical Disclosure Bulletin, Vol. 16, No. 10, March 1974, pp. 3134-5; and U.S. Pat. Nos. 4,241,367; 4,219,855; and 4,190,872.